cas was created for this scenario.
--
Dustin Sallings (mobile)
On Feb 21, 2008, at 13:23, "Rakesh Rajan" <[EMAIL PROTECTED]> wrote:
Hi,
I am using memcached to store a lot of collections. An example would
be, for a given item, a collection of integers representing various
attributes. Now, since there can be concurrent update to the
collection ( addition / deletion / updation ), there are times when
the cached data gets stale/dirty. Example
Current Cache [ 1,2]
Thread 1 ( Added 3 ) : [1,2,3]
Thread 2 ( Added 4 ) : [1,2,4]
Thread 3 ( Removed 2 ) : [1]
Now when all 3 threads tries to update the cache, cache becomes
dirty. One way to solve this is, for every set operation, I would
need to get the current cached collection and then perform operation
( addition/deletion/updation) on it before setting it back ( with
the write operation acquiring a lock first ).
For a typical write, I do
-> Take a lock ( with ~1-2 secs timeout)
-> Fetch the current cache value ( if any)
-> Perform the operation between the cached data and the
newer data ( addition/deletion/updation)
-> Update the cache with the newer collection
-> Release the lock ( this is purely a safety mechanism : in the
finally block of the java code )
So every write operation, I need to make 4 memcached calls which I
believe is not a good solution ( since it is in the same thread).
One possible solution that I was thinking was making the cache
update async process. Would love to hear how this case is generally
solved / opinions ? ( In my case collections are either Set / List )
-Rakesh
